1. Technical Field
The present invention relates to methods, devices, and computer programs for rapidly making, screening, and characterizing an array of materials in which process conditions are controlled and monitored.
2. Discussion
In combinatorial chemistry, a large number of candidate materials are created from a relatively small set of precursors and subsequently evaluated for suitability for a particular application. As currently practiced, combinatorial chemistry permits scientists to systematically explore the influence of structural variations in candidates by dramatically accelerating the rates at which they are created and evaluated. Compared to traditional discovery methods, combinatorial methods sharply reduce the costs associated with preparing and screening each candidate.
Combinatorial chemistry has revolutionized the process of drug discovery. One can view drug discovery as a two-step process: acquiring candidate compounds through laboratory synthesis or through natural products collection, followed by evaluation or screening for efficacy. Pharmaceutical researchers have long used high-throughput screening (HTS) protocols to rapidly evaluate the therapeutic value of natural products and libraries of compounds synthesized and cataloged over many years. However, compared to HTS protocols, chemical synthesis has historically been a slow, arduous process. With the advent of combinatorial methods, scientists can now create large libraries of organic molecules at a pace on par with HTS protocols.
Recently, combinatorial approaches have been used for discovery programs unrelated to drugs. For example, some researchers have recognized that combinatorial strategies also offer promise for the discovery of inorganic compounds such as high-temperature superconductors, magnetoresistive materials, luminescent materials, and catalytic materials. See, for example, co-pending U.S. patent application Ser. No. 08/327,513 xe2x80x9cThe Combinatorial Synthesis of Novel Materialsxe2x80x9d (published as WO 96/11878) and co-pending U.S. patent application Ser. No. 08/898,715 xe2x80x9cCombinatorial Synthesis and Analysis of Organometallic Compounds and Catalystsxe2x80x9d (published, in part, as WO 98/03251), which are all herein incorporated by reference.
Because of its success in eliminating the synthesis bottleneck in drug discovery, many researchers have come to narrowly view combinatorial methods as tools for creating structural diversity. Few researchers have emphasized that, during synthesis, variations in temperature, pressure, ionic strength, and other process conditions can strongly influence the properties of library members. For instance, reaction conditions are particularly important in formulation chemistry, where one combines a set of components under different reaction conditions or concentrations to determine their influence on product properties.
Moreover, because the performance criteria in materials science is often different than in pharmaceutical research, many workers have failed to realize that process variables often can be used to distinguish among library members both during and after synthesis. For example, the viscosity of reaction mixtures can be used to distinguish library members based on their ability to catalyze a solution-phase polymerizationxe2x80x94at constant polymer concentration, the higher the viscosity of the solution, the greater the molecular weight of the polymer formed. Furthermore, total heat liberated and/or peak temperature observed during an exothermic reaction can be used to rank catalysts.
Therefore, a need exists for an apparatus to prepare and screen combinatorial libraries in which one can monitor and control process conditions during synthesis and screening.
The present invention generally provides an apparatus for parallel processing of reaction mixtures. The apparatus includes vessels for containing the reaction mixtures, a stirring system, and a temperature control system that is adapted to maintain individual vessels or groups of vessels at different temperatures. The apparatus may consist of a monolithic reactor block, which contains the vessels, or an assemblage of reactor block modules. A robotic material handling system can be used to automatically load the vessels with starting materials. In addition to heating or cooling individual vessels, the entire reactor block can be maintained at a nearly uniform temperature by circulating a temperature-controlled thermal fluid through channels formed in the reactor block. The stirring system generally includes stirring membersxe2x80x94blades, bars, and the likexe2x80x94placed in each of the vessels, and a mechanical or magnetic drive mechanism. Torque and rotation rate can be controlled and monitored through strain gages, phase lag measurements, and speed sensors.
The apparatus may optionally include a system for evaluating material properties of the reaction mixtures. The system includes mechanical oscillators located within the vessels. When stimulated with a variable-frequency signal, the mechanical oscillators generate response signals that depend on properties of the reaction mixture. Through calibration, mechanical oscillators can be used to monitor molecular weight, specific gravity, elasticity, dielectric constant, conductivity, and other material properties of the reaction mixtures.
The present invention also provides an apparatus for monitoring rates of production or consumption of a gas-phase component of a reaction mixture. The apparatus generally comprises a closed vessel for containing the reaction mixture, a stirring system, a temperature control system and a pressure control system. The pressure control system includes a pressure sensor that communicates with the vessel, as well as a valve that provides venting of a gaseous product from the vessel. In addition, in cases where a gas-phase reactant is consumed during reaction, the valve provides access to a source of the reactant. Pressure monitoring of the vessel, coupled with venting of product or filling with reactant allows the investigator to determine rates of production or consumption, respectively.
One aspect of the present invention provides an apparatus for monitoring rates of consumption of a gas-phase reactant. The apparatus generally comprises a closed vessel for containing the reaction mixture, a stirring system, a temperature control system and a pressure control system. The pressure control system includes a pressure sensor that communicates with the vessel, as well as a flow sensor that monitors the flow rate of reactant entering the vessel. Rates of consumption of the reactant can be determined from the reactant flow rate and filling time.
The present invention also provides a method of making and characterizing a plurality of materials. The method includes the steps of providing vessels with starting materials to form reaction mixtures, confining the reaction mixtures in the vessels to allow the reaction to occur, and stirring the reaction mixtures for at least a portion of the confining step. The method further includes the step of evaluating the reaction mixtures by tracking at least one characteristic of the reaction mixtures for at least a portion of the confining step. Various characteristics or properties can be monitored during the evaluating step, including temperature, rate of heat transfer, conversion of starting materials, rate of conversion, torque at a given stirring rate, stall frequency, viscosity, molecular weight, specific gravity, elasticity, dielectric constant, and conductivity.
One aspect of the present invention provides a method of monitoring the rate of consumption of a gas-phase reactant. The method comprises the steps of providing a vessel with starting materials to form the reaction mixture, confining the reaction mixtures in the vessel to allow reaction to occur, and stirring the reaction mixture for at least a portion of the confining step. The method further includes filling the vessel with the gas-phase reactant until gas pressure in the vessel exceeds an upper-pressure limit, PH, and allowing gas pressure in the vessel to decay below a lower-pressure limit, PL. Gas pressure in the vessel is monitored and recorded during the addition and consumption of the reactant. This process is repeated at least once, and rates of consumption of the gas-phase reactant in the reaction mixture are determined from the pressure versus time record.
Another aspect of the present invention provides a method of monitoring the rate of production of a gas-phase product. The method comprises the steps of providing a vessel with starting materials to form the reaction mixture, confining the reaction mixtures in the vessel to allow reaction to occur, and stirring the reaction mixture for at least a portion of the confining step. The method also comprises the steps of allowing gas pressure in the vessel to rise above an upper-pressure limit, PH, and venting the vessel until gas pressure in the vessel falls below a lower-pressure limit, PL. The gas pressure in the vessel is monitored and recorded during the production of the gas-phase component and subsequent venting of the vessel. The process is repeated at least once, so rates of production of the gas-phase product can be calculated from the pressure versus time record.
The present invention provides an apparatus for parallel processing of reaction mixtures comprising vessels for containing the reaction mixtures, a stirring system for agitating the reaction mixtures, a temperature control system for regulating the temperature of the reaction mixtures, and a fluid injection system. The vessels are sealed to minimize unintentional gas flow into or out of the vessels, and the fluid injection system allows introduction of a liquid into the vessels at a pressure different than ambient pressure. The fluid injection system includes fill ports that are adapted to receive a liquid delivery probe, such as a syringe or pipette, and also includes conduits, valves, and tubular injectors. The conduits provide fluid communication between the fill ports and the valves and between the valves and the injectors. The injectors are located in the vessels, and can have varying lengths, depending on whether fluid injection is to occur in the reaction mixtures or in the vessel headspace above the reaction mixtures. Generally, a robotic material handling system manipulates the fluid delivery probe and controls the valves. The injection system can be used to deliver gases, liquids, and slurries, e.g., catalysts on solid supports.
One aspect of the present invention provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels, a temperature control system, and a stirring system having a magnetic feed through device for coupling an external drive mechanism with a spindle that is completely contained within one of the vessels. The magnetic feed through device includes a rigid pressure barrier having a cylindrical interior surface that is open along the base of the pressure barrier. The base of the pressure barrier is attached to the vessel so that the interior surface of the pressure barrier and the vessel define a closed chamber. The magnetic feed through device further includes a magnetic driver that is rotatably mounted on the rigid pressure barrier and a magnetic follower that is rotatably mounted within the pressure barrier. The drive mechanism is mechanically coupled to the magnetic driver, and one end of the spindle is attached to a leg portion of the magnetic follower that extends into the vessel headspace. Since the magnetic driver and follower are magnetically coupled, rotation of the magnetic driver induces rotation of the magnetic follower and spindle.
Another aspect of the present invention provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels, a temperature control system, and a stirring system that includes multi-piece spindles that are partially contained in the vessels. Each of the spindles includes an upper spindle portion that is mechanically coupled to a drive mechanism, a removable stirrer contained in one of the vessels, and a coupler for reversibly attaching the removable stirrer to the upper spindle portion. The removable stirrer is made of a chemically resistant plastic material, such as polyethylethylketone or polytetrafluoroethylene, and is typically discarded after use.
The exact combination of parallel processing features depends on the embodiment of the invention being practiced. In some aspects, the present invention provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels and an injection system. The present invention also provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels, an injection system and a stirring system. The present invention also provides an apparatus for parallel processing of reaction mixtures comprising vessels having a temperature control system and a stirring system. The present invention also provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels and a pressure control system. The present invention also provides an apparatus for parallel processing of reaction mixtures comprising sealed vessels, an injection system and a system for property or characteristic monitoring.
The present invention also provides computer programs and computer-implemented methods for monitoring the progress and properties of parallel chemical reactions. In one aspect, the invention features a method of monitoring a combinatorial chemical reaction. The method includes (a) receiving a measured value associated with the contents of each of a plurality of reactor vessels; (b) displaying the measured values; and (c) repeating steps (a) and (b) multiple times over the course of the combinatorial chemical reaction.
Implementations of the invention can include one or more of the following advantageous features. The measured values include a set of values for a number of reaction conditions associated with each of the reactor vessels. Step (c) is performed at a predetermined sampling rate. The method also includes changing a reaction parameter associated with one of the reactor vessels in response to the measured value to maintain the reactor vessel at a predetermined set point. Reaction parameters include temperature, pressure, and motor (stirring) speed. The method also includes quenching a reaction in one of the reactor vessels in response to the measured value associated with the contents of the reactor vessel. The method also includes using the measured value to calculate an experimental variable or value for one of the reactor vessels. Examples of experimental variables include rates of change of temperature or pressure, percent conversion of a starting material, and viscosity. The method also includes displaying the experimental variable.
In general, in another aspect, the invention features a method for controlling a combinatorial chemical reactor including multiple reactor vessels, each containing a reaction environment. The method includes receiving a set point for a property associated with each vessel""s reaction environment; measuring a set of experimental values for the property for each vessel; displaying the set of experimental values; and changing the reaction environment in one or more of the plurality of reactor vessels in response to the set point and a change in one or more of the set of experimental values. For example, the method may terminate a reaction (change the reaction environment) in response to reactant conversion (experimental value) indicating that a target conversion (set point) has been reached. During reaction, a graphical representation of the set of experimental values is displayed, often as a histogram.
In general, in another aspect, the invention features a computer program on a computer-readable medium for monitoring a combinatorial chemical reaction. The program includes instructions to (a) receive a measured value associated with the contents of each of a plurality of reactor vessels, instructions to (b) display the measured values, and instructions to (c) repeat steps (a) and (b) multiple times during the course of the combinatorial chemical reaction. The computer program includes instructions to change a reaction parameter associated with one of the reactor vessels in response to the measured value to maintain the reactor vessel at a predetermined set point.
In general, in another aspect, the invention features a reactor control system for monitoring and controlling parallel chemical reactions. The reactor system includes a system control module for providing control signals to a parallel chemical reactor including multiple reactor vessels, a mixing monitoring and control system, a temperature monitoring and control system, and a pressure monitoring and control system. The reactor system also includes a data analysis module for receiving a set of measured values from the parallel chemical reactor and for calculating one or more calculated values for each of the reactor vessels. In addition, the reactor control system includes a user interface module for receiving reaction parameters and for displaying the set of measured values and calculated values.
Advantages that can be seen in implementations of the invention include one or more of the following. Process variables can be monitored and controlled for multiple elements in a combinatorial library as a chemical reaction progresses. Data can be extracted for each library element repeatedly and in parallel over the course of the reaction, instead of extracting only a limited number of data points for selected library elements. Calculations and corrections can be applied automatically to every available data point for every library element over the course of the reaction. A single experimental value can be calculated from the entire data set for each library element.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification, drawings, and claims.